1. Field of the Invention
The present invention relates to an organic dye-sensitized solar cell, a semiconductor electrode of organic dye-sensitized metal oxide advantageously used in the solar cell and the process for the preparation thereof.
2. Description of the Related Art
Recently, great attention has been paid to a solar cell that converting directly the sunlight to electrical energy from the standpoints of energy saving, effective utilization of resources and prevention of environmental pollution, and therefore the development of the solar cell has been advanced.
As the solar cell, those utilizing crystalline silicon or amorphous silicon widely employed. However, a large amount of energy is required to form the crystalline silicon or the like and therefore the use of silicon brings about effect contrary to the original object of the solar cell, that is energy saving cell utilizing the sunlight. Further as a result of the consumption of a large amount of energy, the solar cell using the silicon as a photoelectric conversion material becomes expensive.
The photoelectric conversion material converts light energy to electric energy by the electrochemical reaction caused between electrodes. For example, when the photoelectric conversion material is exposed to light, electrons generate on one of the electrodes and the electrons are moved to the electrode couple (the other of the electrodes). The electrons moved to the electrode couple are changed to ions in electrolyte and returned to the former electrode. Thus the photoelectric conversion material enables light energy to be taken out in the form of electric energy and hence can be utilized as the solar cell.
A solar cell using semiconductor of dye-sensitized metal oxide instead of silicon as a photoelectric conversion material is already known. Nature, 268 (1976), page 402 describes a solar cell having a semiconductor electrode of dye-sensitized metal which is prepared by subjecting zinc oxide powder to compression molding, sintering the molded powder at 1,300° C. for one hour to form a disc-shaped sintered product and adsorbing Rose Bengal as an organic dye on the sintered product. In the electric current/voltage curve of this solar cell, the electric current in electromotive voltage of 0.2V is extremely low approx. 25 μA, and therefore it is little possible to put the solar cell to practical use. However, in contrast with the solar cell using silicon, the semiconductor of metal oxide and organic dye used in this solar cell are manufactured in large quantity and the they are relatively at low price. Therefore this solar cell is greatly advantageous in view of the used materials.
As the solar cell using a semiconductor of dye-sensitized metal oxide as a photoelectric conversion material, in addition of the above-mentioned solar cell, there are known the followings: a solar cell having a layer of spectral sensitizing dye such as a transition metal complex provided on a surface of the semiconductor layer of metal oxide, which is described in JP-A-1-220380, and a solar cell having a layer of spectral sensitizing dye such as a transition metal complex provided on a surface of the semiconductor layer of metal ion-doped titanium oxide, which is described in JP-A-5-504023.
The above-mentioned solar cells do not show practically satisfactory electric current/voltage curve. JP-A-10-92477 discloses a solar cell showing practically satisfactory electric current/voltage curve, which has an oxide semiconductor layer comprising the sintered product of the aggregation of fine particles of oxide semiconductor. The layer is formed by applying a slurry of fine particles of oxide semiconductor onto a transparent electrode, drying the slurry film and sintering the dried film at 500° C. for approx. one hour.